Packt Publisher has published an ebook called Instant Apple iBooks Howto. This is a useful and comprehensive summary of first how to use the iBooks reader app and then how to use the iBook author app. The book has thorough and straight to the point coverage of these apps which includes generous screen shots throughout to make it easy to follow along.
The information is well organized and an example is provided to demonstrate the concepts and features. The example is a London City Guide and it is available for download to examine exactly how it was put together.
The book is pretty much aligned to its title in that it gives you a straight to the point quick summary on how to use iBook and iBook Author. By showing how easy it really is to create an ebook it will hopefully encourage aspiring authors to give it a try.